The present invention relates to a power limiter for the high microwave range, formed from several PIN diodes of the silicon type which are mounted in a waveguide and operate for millimeter waves, as well as to a method of making these diodes.
It will be recalled that the purpose of a device of this kind is to transmit particular microwave signals with a minimum power loss and to separate particular signals from the others.
FIGS. 1 and 2 respectively illustrate a perspective view and a cross-section view along the line II--II of a known structure of a high-power limiter comprising silicon PIN diodes for millimeter waves, as described in the article published in "Microwave Journal", March 1983, pages 65 to 70, entitled "Millimeter wave high power solid state limiter". This limiter 1 is formed by a rectangular metal waveguide 2, having the longitudinal axis .DELTA., of dimensions permitting the propagation of millimetric waves, and wherein is mounted transversely to the axis .DELTA. a substrate 3 of silicon in the form of a parallelepipedic strip or blade having a rectangular cross-section of the same dimensions as those of the cross-section of the guide, for example L.sub.1 =2.54 mm and L.sub.2 =1.27 mm.
So that these may withstand a high level of microwave power, several silicon PIN diodes 5 of identical size, for example four in number, are formed in the surface of the substrate 3 in a series-parallel configuration, and are situated facing the input of the incident power P.sub.e to assure limitation of the latter. The silicon substrate 3 has a dimension L.sub.3 along the longitudinal axis .DELTA. of the guide of the order of 100 microns and obstructs a cross-section of the guide 2.
In FIG. 2, the production of the PIN diodes 5 in the surface of the silicon substrate 3 of a thicknesss L.sub.3 of the order of 100 microns, is effected initially by acting on this latter in a manner such as to form grooves of a depth of the order of 20 microns, delimiting the intrinsic silicon areas I of the diodes while leaving a deep zone 7 of silicon in parallel on the zones I of the diodes, thus of the order of 80 microns. The action on the substrate is followed by alternate conventional diffusions of the P.sup.+ N.sup.+ types performed at the level of the grooves, thus forming the P.sup.+ and N.sup.+ zones of the different diodes produced in this manner. The grooves are then covered with metallizations 8 forming contacts on the alternate P.sup.+ and N.sup.+ areas of the diodes 5, and two metal bus connectors respectively interconnect the anode and cathode metallizations of the diodes. Only the bus interconnecting the anode metallizations is needed in the example chosen and illustrated in FIG. 2, and is denoted by the pecked lines 9 in this Figure. The PIN diodes 5 are biased by applying an external voltage .+-.V (FIG. 1) between the two metal bus connectors.
However, a high power limiter for millimeter waves according to this prior art has disadvantages. In fact, the presence of the silicon zone in parallel with the zones I of the diodes formed in the silicon substrate creates a lagging of the carriers injected into the areas I of the diodes, which appreciably increases the switching period of the millimeter waves being propagated within the waveguide. As a result, these switching PIN diodes cannot be described as fast diodes. Furthermore, this area of silicon situated outside the PIN diodes as such introduces supplementary insertion losses at low level and zero polarization.